Preheat oven to 350 degrees. Grease a small (about-9 inch long) loaf pan and set aside. Combine zucchine and banana in a mixing bowl. Mash extremely well, until there are no banana chunks present. Add cocoa powder, sugar, stevia, vanilla, and cinnamon. Stir until completely combined. In another bowl, combine flour, baking powder, baking soda, and sea salt. Whisk the mixture well. Add the dry ingredients to the wet ones in 3-4 batches, stirring well in between each addition. Pour the mixture into the loaf pan, making sure to distribute evenly throughout the pan and smooth over the top. Bake for about 35 minutes. Test by inserting a toothpick; if it comes out clean, it's done.